What does the compass in an aircraft primarily indicate?

The compass in an aircraft primarily indicates heading, which is the direction in which the aircraft's nose is pointing relative to magnetic north. This information is crucial for navigation, allowing pilots to determine their course and make adjustments as necessary to maintain their intended flight path. A heading indication helps pilots align the aircraft with their flight plan and manage turns effectively.

Other options, like altitude, speed, and rate of climb, are measured by separate instruments such as the altimeter, airspeed indicator, and vertical speed indicator respectively. These instruments serve different purposes in flight operation and do not provide heading information. Therefore, the compass is specifically designed to communicate the aircraft's heading, making it an essential tool for navigation.